Hi Fordfanatics,
I asked this on the Expedition Forum and didn't get a thorough response.
I've got an '00 EB Expedition with 4.6/2V/4R70W/8.8 with 3.31 gears.
Therein lies my question-why did Ford pair a small (281ci) engine, heavy SVU with close to 32" tires AND 3.31 gears??????? This makes no sense to me!!!
All the ratio calculators state that a R & P ratio of 4.10/4.11 is optimal for this size tire. The reason for my post is my Expy is SO sluggish and gets 13.8 mpg, city and 14.7, hwy. If I'm getting that kind of terrible performance, I might as well lower the ratio to, at least, 3.73's. My concern is that I'm missing something. Did Ford design this engine/trans/axle/tire combo to be a dog or is this one of those "Ford" goofs?

 

Ford has to think about overall fleet mileage, so that is why they sometimes appear to make decisions that seem crazy on the surface.

The 4R70W has an OD ratio of 0.78:1. With 32" tires and 3.31 gears at 70 MPH, it will spin at about 1900 RPMs. That's going to give you good highway mileage, but you'll probably see it downshift going up any significant hill.

If you swap to 4.10 gears, it will see 2350 RPMs under the same conditions. You will have much more power at your disposal, but highway mileage could go down, stay about the same, or even go up. It can go up because the transmission doesn't have to downshift as often, which saves fuel (and wear and tear on the transmission). It really depends on driving conditions and driving habits.

Bottom line, I wouldn't expect to see a big change in mileage. Your mileage, as they say, may vary. If you wanted to change gears for more towing capacity and more power, you're on the right track.

 

I'm leaning more towards 3.73's than 4.10's. Didn't Ford have a 3.90 ratio available-or is that 9" territory? My primary goal is better city "feel", but my secondary goal is better mpg's. I theorize that lowering ratios will give me better throttle response AND better mpg's because the motor will struggle LESS with the compounding of gears.

 

I'd think you would be happy with 4.10 gears.

That ratio compares very closely to what my old explorer had with 3.73 gears and shorter tires. It gave really good overall performance, imo.

The only thing I didn't like was that the engine was spinning 3,000 rpm at 65mph when running in third (towing) which just took some getting used to, and didn't make me want to go any faster. It did tow very well, though while running that kind of engine speed.

I dont think you are missing anything. They put tall gears in for fuel mileage, but in reality it didn't help much, if at all.

If you are willing to spend the money and don't mind the higher rpm while towing in 3rd, I think you would be happy with that set up.

If you ever had a mind to go to a bigger tire like the newer ones, (265/70r17 or 265/75r16), then 4.30s would be the gear to go, imo. 4.30's with that size tire is about the same as 4.10's with your current size.